西双版纳热带雨林土壤与叶片生态化学计量特征的干湿度效应

基于地理格局对西双版纳热带雨林的干湿度梯度效应和生态化学计量学的研究思路,结合野外试验监测和室内分析,对西双版纳热带雨林土壤-植物系统元素化学计量特征对海拔和干湿度效应响应进行了研究探讨,结果发现:西双版纳热带雨林土壤和叶片碳氮磷化学计量特征均不同程度的受到海拔和干湿季影响。季雨林与山地雨林的水热梯度受海拔梯度重要影响,随海拔梯度升高,土壤含水率变化显著,且含水率在干湿季均对土壤有机碳(SOC)存在显著影响(P0.01),雨季其对土壤全氮(STN)和土壤全磷(STP)的影响要显著于干季;叶片全磷(TP)随含水率的增大而升高,而叶片全氮(TN)在干季会随含水率的升高而增大,雨季含水率升高到一定程度时会抑制TN含量的增加并出现单峰现象;而土壤C/P与海拔和干季土壤含水率的极显著相关性(P0.01)及干季叶片C/N与叶片含水率的显著相关关系(P0.05)说明,干季水分匮乏条件下,土壤含水率影响土壤P的矿化度和植物对P的吸收利用水平,而且叶片C/N对反馈植物水分含量具有明显指示作用。因此,水热梯度是土壤-叶片系统碳氮磷生态化学计量特征变化的重要驱动因素。此外,全球变化区域响应方面,多雨高温可能会削弱季雨林叶片C的同化能力,且叶N含量降低,但受氮沉降的影响,对C/N的影响尚无法确定;由于P循环对其他元素的耦合作用,雨林土壤-叶片系统的元素循环周期将会被缩短,但干季山地雨林植物生态系统P的限制作用有可能会减弱。

Effect of the humidity/aridity gradient on the ecological stoichiometry of soil and leaves in Xishuangbanna tropical rainforest

This study investigated the humidity/aridity gradient effects and ecological stoichiometry in Xishuangbanna tropical rainforest. The geographical pattern, characteristics of ecological stoichiometry and its response to altitude and humidity/aridity effects were studied in the soil and plants of Xishuangbanna tropical rainforest using field and laboratory analyses. The results showed that the ecological stoichiometry of soil and leaves in Xishuangbanna rainforest was influenced by altitude and humidity gradients, to varying degrees. The hydrothermal gradient of seasonal and montane rainforests was affected by altitude. The soil moisture content had a significant effect on soil organic carbon (SOC) (P < 0.01) in dry and wet seasons, which was significantly controlled by the altitude gradient. The effect of soil moisture content on soil total nitrogen (STN) and soil total phosphorus (STP) was more significant during the rainy season. The total phosphorus (TP) content in leaves increased with increasing water content, and the variation trend of leaf TN content in the dry season was consistent with the TP content. However, water content reduced the total nitrogen (TN) content when it increased to a certain extent during the rainy season. The significant correlation among soil moisture in the dry season, altitude, and the C/P of soil, similar to the correlation between C/N and water content of leaves in the dry season, indicated that the level of soil water content determines the mineralization of soil phosphorus and the ability of plants to absorb P under the water shortage. Leaf C/N has obvious implications for the feedback moisture content of plants. This further illustrates that the hydrothermal gradient is an important driver for the stoichiometry characteristics of soil-leaf ecosystems. Additionally, high temperature and rain may weaken the assimilation capacity of leaf C content in a seasonal rainforest, and leaf N content may decrease in terms of regional response to global change. Furthermore, the elemental cycles of soil-leaf systems would be shortened, and the dry season may weaken the limiting effect of P in plant ecosystems of montane rain forests because of the coupling effects of P cycles to other elements.